1. Field of the Invention
The present invention relates to an optical gain waveguide doped with Er element, and a method of controlling the same.
2. Related Background Art
An optical gain waveguide, whose optical waveguide region is doped with Er element, is, for example, an optical waveguide such as an optical fiber. In the optical waveguide, pumping light with a wavelength capable of pumping the Er element is propagated, as well as C-band signal light to be amplified. In general, as pumping light for pumping the Er element, pumping light with the 0.98-μm wavelength band is used (for example, refer to Documents 1 and 2). Further, in a WDM (wavelength division multiplexing) optical transmission system, the gain spectrum of the above optical gain waveguide has desirably excellent gain flatness in a wider wavelength band (that is, small gain variations in a wider wavelength band of the signal light), when taking into consideration the cases of collectively amplifying signal light of a plurality of channels mutually having different wavelengths.
Document 1: U.S. Pat. No. 6,621,624
Document 2: A. J. G. Ellison, et al., “Hybrid Erbium Silicate Conventional-Band Fiber Amplifier with Ultra-Low Gain Ripple”, OAA1999, Postdeadline papers 2 (1999)
Document 3: K. W. Bennett, et al., OAA1997, Postdeadline papers 4 (1997)
Document 4: S. Shen and A. Jha, Optical Materials, vol. 25, pp. 321-333 (2004)